It is already known to use in connection with taxis indicator means which are adapted to show whether a taxi is vacant and therefore available for hire or whether it is engaged and thus unavailable for hire.
Such an indicator serves a useful purpose in that persons wishing to hail a taxi can readily do so when a sign is displayed that the taxi is vacant, and of course there are cases where a taxi may be stationary but engaged and on such condition it is again advantageous to be able to display that the taxi is not for hire.
The method usually adopted for such a device is to have an indicator within the taxi itself which is visible through perhaps the windscreen and which can be set by the operator to show either the sign "Vacant" or "Not for Hire," but such a device is not readily visible because of its location and there is now a requirement for the unit which will be more readily visible to persons wishing to hire a taxi yet which will be simple to operate and will provide the required information.